Hello,
In order to use integral-evaluate-spline, I had to modify its
definition. The one below works, but I am not sure if there is a
better way. Here is the definition:
(defmfun integral-evaluate-spline (spline xa ya low high acceleration)
"gsl_spline_eval_integ"
(((mpointer spline) :pointer) ((c-pointer xa) :pointer) ((c-pointer
ya) :pointer) (low :double) (high :double)
((mpointer acceleration) :pointer))
:c-return :double
:documentation ; FDL
"Find the numerical integral of an interpolated function over the
range [low, high], using the spline object spline,
data arrays xa and ya and the accelerator acceleration.")
I removed a reference to a double-float `x' and added the x&y array
pointers into the arguments, as they are necessary for gsl's
`gsl_interp_eval_integ'.
(I am really not sure what is the purpose of the ..._e functions).
Here is a bit of test code that exercises the defintion by integrating
pi*sin(pi x) between 0 & 0.5 which should equal 1.0:
(let* ((acc (make-acceleration))
(xarr
(make-marray
'double-float
:initial-contents
(loop for i from 0.0d0 below 1d0 by 0.2d0
collect i)))
(yarr
(make-marray
'double-float
:initial-contents
(loop for x across (cl-array xarr)
collect (sin (* x pi)))))
(spline (make-spline *cubic-spline-interpolation* xarr yarr)))
(* pi (integral-evaluate-spline spline xarr yarr 0d0 0.5d0 acc)))
I wonder if there is a way for `make-spline' to "remember" xarr and
yarr so they don't have to be passed to `integral-evaluate-spline'.
As always, thank for the heavy lifting :-)
Mirko